Printbars are used in printer systems to optically expose regions on a photoreceptor on which a marking material, such as a toner, is to be deposited. Modern printers often use an array of Light Emitting Diodes (hereinafter LEDs) on a printbar to illuminate areas on which to deposit the toner. Each area illuminated by an LED corresponds to a xe2x80x9cpixelxe2x80x9d or xe2x80x9csubpixelxe2x80x9d of deposited toner. For an ideal printed image, these printed pixels or subpixels should be of uniform in size.
Pixel size and darkness is partially determined by the amount of light emitted by the LED corresponding to the pixel. In order to ensure uniformity of the printed pixels, it is important that each LED on a printbar outputs an intensity that is similar to other LEDs on the printbar. Thus, during assembly of the printbar, power sources providing power to the LEDs compensate for the non-uniformities between different LEDs in the printbar.
Almost immediately after being set in the factory, each LED in the printbar starts aging at a different rate. The different rates of aging and other changes to the LEDs and the drive systems results in a slow deterioration of printer output as non-uniformities in LED output increases in time. These nonuniformities produce uneven print results. When non-uniformities reach an unacceptable level, the printbar is replaced even though the LEDs in the printbar may have a substantial useful remaining life. Because of the high cost of printbars and the service personnel time used to replace the printbar, such replacements represent a significant waste of resources.
A system, incorporated into a printer, to monitor the LED printbar and automatically correct for deterioration of the LEDs is described. The system includes at least one detector integrated into the printbar to detect the output intensity of each LED in the printbar. Each LED output is compared to a reference output. When a LED output varies from the reference by more than a predetermined amount, a power supply or electrical driver that provides power to the LED is recalibrated to cause the LED to output the referenced intensity.